Exterior windows and doors in secure facilities face two kinds of exposure: the threats they were designed to stop, and the environmental conditions they have to outlast. Wind-driven rain, freeze-thaw cycles, and prolonged moisture exposure can degrade seals, accelerate frame corrosion, and affect hardware function over time.
ASTM E331 is the test standard that verifies an exterior assembly resists water penetration under those conditions.
What Is ASTM E331?
ASTM E331 is the Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference, published by ASTM International.
It measures whether an exterior assembly allows water to penetrate under a controlled combination of a water spray system and air pressure. The test is typically performed in a laboratory setting before a product is specified or installed.
A related standard, ASTM E1105, covers field determination of water penetration for assemblies that are already installed. E331 is the laboratory test. E1105 is used on-site.
How This Standard Test Method for Water Penetration Works
During testing, the assembly is mounted in a test chamber. A spray rack with calibrated nozzles delivers water to the outdoor face and the assembly's exposed edges simultaneously.
At the same time, a uniform static air pressure difference is applied with pressure higher on the outdoor face than on the indoor face, simulating wind-driven rain conditions. The air pressure difference is applied within 15 seconds of the spray reaching the specified rate, and both conditions are maintained for 15 minutes.
The result is based on the presence or absence of water penetration through the test specimen. An investigator observes and records findings throughout. Because the test is standardized and repeatable, results can be used for comparison across different assemblies and included in submittal documentation.
Where Is ASTM E331 Applicable?
ASTM E331 applies to any exterior window, curtain wall, skylight, or door assembly. For ballistic framing projects, it becomes a relevant consideration in several scenarios:
- Energy code compliance. Projects subject to ASHRAE 90.1, the International Energy Conservation Code (IECC), or California's Title 24 may require documented water resistance performance as part of fenestration submittals.
- Climate-sensitive installations. Facilities in regions with significant wind-driven rain, high humidity, or hard freeze-thaw cycles benefit from frames with verified water resistance to protect long-term seal and hardware integrity.
- Institutional submittal requirements. Government, municipal, and commercial projects often require third-party verified performance data. Documented ASTM E331 compliance supports the approval process.
Whether this standard is applicable to your project depends on the system, application, and local requirements.
ASTM E331 Is Part of the Testing for TSS Thermally Broken Frames
TSS's thermally broken framing system (650 TB) is engineered for exterior applications where ballistic protection and building envelope performance are required. ASTM E331 is one of several standards the 650 TB has been tested to, alongside:
- UL 752 Standard for Bullet Resistant Materials
- ASTM E283 Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows and Doors
- ASTM B221 Standard Specification for Aluminum and Aluminum Alloy Extruded Bars, Rods, Wires, Profiles and Tubes
- ASTM B209 Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
The 650 TB includes a non-conductive polyamide thermal break between the interior and exterior sections of the aluminum frame. This reduces the temperature differential across the frame, which helps minimize condensation and the seal degradation that follows. The system is available in configurations tested to UL 752 Levels 3 through 8, fits bullet-resistant glazing from 1¼" to 3¼" thick, and is offered in clear or dark bronze.
For exterior installations in demanding climates, the 650 TB gives specifiers a single system with documented ballistic, air, and water performance.
Frequently Asked Questions About ASTM E331
Is ASTM E331 required by building codes?
ASTM E331 is a test method, not a code requirement. Many building codes and energy standards reference it as the accepted means of verifying water resistance for exterior windows and doors. Whether it is required on a specific project depends on the jurisdiction, building type, and applicable energy or performance codes.
What is a passing result for an ASTM E331 test?
The standard defines pass/fail based on the presence or absence of water penetration through the assembly while consistent air pressure and water spray are applied over the duration of the test. There is no universal performance threshold built into the standard. Acceptable performance for what the test method covers is defined by the applicable building code, project specification, or criteria established by the design team.
How does ASTM E331 relate to ASTM E283?
ASTM E283 measures air leakage through an exterior assembly, while ASTM E331 measures water penetration. The two standards are often referenced together for exterior fenestration projects where both air and water performance need to be documented. TSS's 650 TB thermally broken framing system has been tested to both.
What is the difference between the penetration testing of exterior windows and curtain walls?
The test method for water penetration resistance is the same for both. The distinction is in how each assembly is constructed and installed. Exterior windows are typically set into a framed opening in the wall, while curtain walls are non-structural cladding systems that span multiple floors and carry only their own weight. Both are subjected to the same controlled water spray and air pressure difference during testing, and both are evaluated on the same pass/fail criteria.
Are bullet-resistant exterior windows tested differently from standard exterior windows?
The ASTM E331 test method is the same regardless of whether the assembly is standard or bullet-resistant. However, bullet-resistant exterior windows present unique design considerations. The glazing is significantly thicker and heavier, which affects frame design, seal selection, and the overall assembly. A framing system needs to be specifically engineered for those conditions to perform reliably in both ballistic and weather resistance testing.
Related Resources
Our goal is to help you make informed decisions that protect your people, secure your assets, and support your mission—without sacrificing design or functionality. These resources offer guidance for your project.
Ballistic Door Solutions Guide
10 Things That Make Or Break a Bullet-Resistant Barrier Project
Guide To Improving Physical Security By Addressing The Human Factor
